Direct Electrolytic Reduction of Powdery SiO_2 in Molten CaCl_2 with Pellet-type SiO_2 Contacting Electrodes

摘要

Direct electrolytic reduction of powdery SiO_2 has been investigated in molten CaCl_2 at 1123 K aiming at a low-cost production of solar-grade Si. Pellet-type SiO_2 contacting electrodes composed of a palletized SiO_2 powder and a lead material of a Si rod or a Pt wire were newly contrived, and the impurity levels of the produced Si were evaluated. A two-electrode method was also applied, which considerably lowered impurity levels of metal elements in the produced Si. The concentrations of impurities contained in the original SiO_2 powders, the prepared SiO_2 pellets and the electrolyzed samples were traced with ICP-AES and GDMS analyses. It was revealed that B and P concentrations were not significantly increased in the electrolysis. Another pellet-type SiO_2 contacting electrode, in which three pellets composed of SiO_2 and Si powders were attached to a Si rod, was also devised for the improvement of reduction rate.